Field: The invention is in the field of colloid osmometers, sometimes referred to as oncometers, for measuring oncotic or colloid osmotic pressures, e.g. of blood by medical laboratories to determine the presence of pulmonary edema that could cause heart failure.
State of the Art: The measurement of oncotic or colloid osmotic pressures of solutions of substances having high molecular weights, e.g. of blood proteins constituting colloids in colloidal blood solutions such as blood plasma or serum, and instruments for accomplishing same have been described by Theodore R. Reiff and Marvin J. Yiengst in a paper entitled "A Rapid Automatic Semimicro Colloid Osmometer", published in the Journal of Laboratory and Clinical Medicine, Vol. 53, No. 2, pp. 291-298, Feb. 1959, and by Max Harry Weil et al. in a paper entitled "routine Plasma Colloid Osmotic Pressure Measurements", published in Critical Care Medicine, Vol. 2, No. 5, pp. 229-234, September-October 1974. Bisera et al. U.S. Pat. No. 4,028,931, issued June 14, 1977, entitled "Osmotic Pressure Sensing Head" discloses an improved sensing head for such an instrument. These all employ a sample chamber and a corresponding reference chamber that confront each other through a spot-like area of an intervening osmotic membrane. The patented improvement directs the incoming flow of sample solution onto the membrane at an angle such that debris is flushed from the corresponding surface of the membrane.
For many years there has been on the market a similar instrument produced by David E. Burge, doing business as Wescan Instruments, Santa Clara, Calif. There, however, the sample chamber and corresponding reference chambers are narrow and elongate and extend over a zigzag path of considerable length having numerous abrupt, right-angle turns. Solution is introduced at one end of the path in each chamber and withdrawn at the other end of the path.
Objectives: In the making of the present invention, it was a principal objective to provide considerable contact area for the sample and reference solutions with the osmotic membrane, while minimizing pressure response time. Further objectives were to provide for good flushing action within the sample chamber during cleaning thereof following each use of the instrument, to insure accuracy of results in the making of measurements, and to provide for easy replacement of the membrane when necessary.